Ultrasonic inspection of seal integrity of bond lines in sealed containers

ABSTRACT

A method for determining bond integrity of a sealed package has a lid bonded to a container rim by detecting flaws in the bond between the lid and the container. The method comprises: i) positioning the container rim between an ultrasonic transmitter system and an ultrasonic receiver system; ii) ultrasonically coupling the transmitter system and the receiver system to the container rim; iii) transmitting ultrasound waves from the transmitter system through the container rim to the receiver system; iv) generating a signal representative of the ultrasound waves received by the receiver system; and v) analyzing the signal for predetermined signal characteristics representative of a flaw in the bond to identify a flawed package seal.

FIELD OF THE INVENTION

This invention relates to the non-destructive testing of bond integrityof a sealed package having a lid bonded to the container rim.

BACKGROUND OF THE INVENTION

A variety of containers are used to package substances which aresensitive to air to ensure extended shelf-life of the contained product.The seal for the lid of the container must be complete to ensureviability of the contents. This is particularly important in the fieldof packaging food and other comestibles and medical products and thelike. Containers, which are particularly sensitive to defects incontainer seal, are those containers where a lid is welded or glued tothe container rim. Such types of containers are used for packaging avariety of food products, such as meal portions, pet foods, dairyproducts and the like, as well as liquids usually in the form ofmedications and cosmetics.

There are presently available a variety of techniques which may be usedto test the integrity of the container seal to ensure extended shelflife of the contained product. Such testing procedures includeapplication of a pressure differential to the container exterior andthereby ascertain whether or not there are leaks at the bond of the lidto the container. The pressure differential may be applied by eitherdrawing a vacuum on or applying pressure to the container. This testingprocedure only works with rigid or semi-rigid containers. Softcontainers are either crushed or blowout. Container defects may also bedetermined by way of costly visual inspection which cannot checkinternal aspects of the seal. X-ray imaging may also be used, but is ofquestionable worth and does not work with aluminum laminates.

It has been suggested in the publication R and D, Selman, J. D. "On-LineDetection of Food Container Faults" February, 1987, that opticalequipment could be used to provide measurement of the seam dimensions byuse of fibre optics systems or lasers to detect seal faults.Thermo-imaging is another technique that may have application indetermining flaws in the seal, but it has been found to be tooinsensitive. The thermal properties of trapped defects, such as meatfibres and bond line materials, are similar. It is also suggested inthis reference that ultrasonics could be used to measure the internalseam bond structure of the lidded container. There is no discussion,however, in the reference of the manner in which ultrasonic testingequipment could be used in detecting flaws in the seal of the container.

Published U.K. patent application 2,029,960 (Mar. 26, 1980) discloses anultrasonic testing device for testing claddings, solder joints, adhesivepoints other types of surface connections. The device is particularlysuited for testing solder joints. A transmitting transducer is coupledto the bonded surface via coupling medium. On the other side of thebond, a receiving transducer is coupled via a coupling medium. Adaptorsmay be used to conform to the geometric shape of the bonded item. Thereceived ultrasonic sound is converted into a signal which is displayedby the apparatus as a sound intensity. A drop in sound intensityindicates that the bond is not complete and hence faulty.

Langrock et al disclose in a report from the Central institute forWelding Technology of the DDR in Halle entitled "Possibilities ofTesting Lap-Welded Joints in Thermoplastic Sealing Strips" that areflective form of electrosonic tester unit would be useful in detectingfaults in lap-joints of plastic material. Pulse wave forms generated bythe testing equipment are analyzed to detect defects in the weldedlap-joint of similar plastic materials. The pulse echo mode of operationis effective with this type of lap-joint in view of the thickness of thefilms which can be in excess of 1 to 2 mm. By analyzing the reflectionof the ultrasonic energy, evaluation can be made in the uniformity ofthe lap-joint in the sealed plastic surfaces. However, the echo systemwould not be sufficiently sensitive to detect very fine defects in thejoint, such as experienced in containers where meat fibers and otherfood fibers can be caught between the bond of the lid to the containerwhich constitutes forming a defective seal. Compared to thesethicknesses, the containers in question have a welded plastic thicknessof only 15 μ with a total seam thickness of only 185 μ.

SUMMARY OF THE INVENTION

According to an aspect of the invention, a method is provided fordetermining bond integrity of a sealed package having a lid bonded to acontainer rim by detecting flaws in the bond between the lid and thecontainer. The method comprises:

i) positioning the container rim between an ultrasonic transmittersystem and an ultrasonic receiver system;

ii) ultrasonically coupling the transmitter system and the receiversystem to the container rim;

iii) transmitting ultrasound waves from the transmitter system throughthe container rim to the receiver system;

iv) generating a voltage signal representative of the ultrasound wavesreceived by the receiver system; and

v) analyzing the voltage signal for predetermined signal characteristicsrepresentative of a flaw in the bond to identify a flawed package seal.

According to another aspect of the invention, an apparatus fordetermining bond integrity of a sealed package has a lid bonded to acontainer rim. The apparatus comprises:

i) spaced-apart opposing ultrasonic transmitter system and an ultrasonicreceiver system;

ii) means for positioning a container rim between the ultrasonictransmitter system and the ultrasonic receiver system; and

iii) means for ultrasonically coupling the transmitter system and thereceiver system to a container rim.

BRIEF DESCRIPTION OF THE DRAWINGS

Preferred embodiments of the invention are shown in the drawingswherein:

FIG. 1 is a schematic flow chart of a container being loaded withproduct, tested and then either passed or rejected;

FIG. 1A is an enlarged view of a section of the container rim;

FIG. 2 is a section through an apparatus in which the method of thisinvention is employed to ultrasonically test the integrity of thecontainer seal;

FIG. 3 shows an alternative embodiment for ultrasonically coupling thesensors to the container rim for purposes of detection;

FIG. 4 shows yet another alternative embodiment for ultrasonicallyconnecting the sensors to the container rim;

FIG. 5 is a perspective showing a container and an array of a pluralityof ultrasonic transmitters and ultrasonic receivers for testing flaws inthe container rim;

FIGS. 5A, 5B, 5C and 5D are view of alternative arrangements for thetesting system of this invention;

FIG. 6 shows a single ultrasonic transmitter and receiver between whichthe container rim is positioned and rotated to sense flaws around theentire periphery of the container rim;

FIG. 7 is perspective view of an apparatus for positioning the singletransmitter and receiver of FIG. 6 and a platform on which the containerrests and is rotated to sense the entire perimeter of the container;

FIG. 8 is a block diagram representing the electronic components forgenerating and analyzing signals from the ultrasonic transducers; and

FIGS. 9(A,B), 9(C,D) and 9 (E,F) are representative signals derived fromtesting containers with and without seal defects.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

There are a variety of packages in which the contents are very sensitiveto its environment. Not only is it important to provide a package inwhich the seal is assured, but also to guarantee extended shelf life,there needs to be a testing technique to determine the integrity of theseal. The testing technique is preferably performed in a non-invasivemanner and also in a way which does not have the potential of destroyingor weakening the seal in the process of analyzing seal integrity.According to this invention, a non-invasive ultrasonically basedtechnique is provided. The purpose of the technique is to determine ineach sealed container the integrity of the seal. If the seal passes, thecontainer is directed for packaging whereas if the seal is flawed ordefective, the container is directed for discard.

As shown in FIG. 1, a container 10 has loaded therein a product 12which, in one way or another, is sensitive to the atmosphere orenvironment in which it is normally placed. The next step is to seal thecontainer 10 with a lid 14. In this embodiment, the container 10 has acircumferential rim 16 with the lid 14 applied to the rim 16 and bondedthereto. The lid 14 is of a size to at least cover the circumferentialdimensions of the container rim 16. The sealed container 18 may have thelid 14 sealed to the container 10 by adhesives, welding of likematerials or other known techniques in bonding of materials such ascatalyzed polymerization of the similar mating materials. As shown inFIG. 1A, according to this particular embodiment, the sealed container18 has a foil lid 20 and a foil container 22. Laminated to the opposingfoils 20 and 22 are thin layers of polypropylene 24 and 26. The opposinglayers of polypropylene 24 and 26, or other suitable polyolefins such aspolyethylene, are heat welded together under pressure to bond the lid 14to the container rim 16. The integrity of the bond between plasticlayers 24 and 26 has to be determined in accordance with the apparatusand method of this invention. The container 18 is conveyed schematicallyto a testing system 28.

According to this embodiment, the perimeter of the container rim withthe lid bonded thereto is placed between a system of ultrasonictransducers in the form of an array of a plurality of ultrasonictransmitter units generally designated 30 and ultrasonic receiver unitsgenerally designated 32. The ultrasonic transmitters and receivers areultrasonically coupled to the container rim in a manner, for example, asdiscussed with respect to the embodiments of FIGS. 2 through 4. Theultrasonic waves are transmitted through the container rim from thetransmitters 30 to the receivers 32. A signal from each receiver is thengenerated representative of the ultrasonic waves received by thereceiver. The signal is analyzed for predetermined signalcharacteristics representative of a flaw in the bond to identify aflawed seal. Hence when the container leaves the sensing system, if thecontainer is not flawed such as sealed container 18a, it is moved in thedirection of arrow 34. If the container 18f is flawed as indicateddiagrammatically in FIG. 1 by exaggerated bump by food residue in theseal at 36, then the container is conveyed in the direction of arrow 38.It is noted that, with the flaw in the seal of container 18f, the flawhas been exaggerated for purposes of illustration. Normally, flaws arenot visible except when adherent food has been squeezed out through theseal. The good container 18a is then conveyed to a suitable packagingtransport station. The flawed container 18f is conveyed for disposal.

One suggested arrangement for detecting flaws in the container rim isshown in FIG. 2. The sealed container 18 is inverted and placed withinan apparatus 38 where a liquid, preferably water, is used toultrasonically couple the transmitter array 30 to the container rim 18and also ultrasonically couple the receiver array 32 to the containerrim 18. The container rim 16 rests on a ledge 40 which is in the shapeof a container rim to thereby support the seal container 18 in theinverted position. The array of ultrasonic receivers 32 are secured inthe block 42 of the apparatus which are supported by feet 44 and 46. Aclosure 48 for the apparatus is provided in which the transmitter array30 is mounted. The probe portions of the transmitters and receiversextend into the space 50 which is filled with water or other suitableliquid. The water is introduced through ports 52 around the perimeter ofthe apparatus. Suitable valves, not shown, are provided in the conduitsfor the ports 52 to control flow of water into the space 50. A drain oroutlet 54 is provided to drain the water from the space 50. A suitablevalve may be located in the drain 54 to control flow of fluid throughthe drain. It is appreciated that all valves associated with the inletsand drains may be electronically controlled so that the sequence infilling the space with water and draining and maintaining water in thespace during testing is all controlled automatically. With the apparatus38 sealed and water ultrasonically coupling the transmitters andreceivers to the container rim, ultrasonic waves are transmitted throughthe container rim and a signal generated based on the waves received bythe receiver 32. The signal generated will be discussed with respect toFIGS. 8 et seq. It has been found that the use of water in the apparatus38 provides an excellent ultrasonic coupling of the transmitter andreceiver to the container rim.

It is appreciated, however, that other systems are available forultrasonically coupling the probes of the transmitters and receivers tothe container rim. As shown in FIG. 3, the individual transmitter 30a isultrasonically coupled to the container rim 16 by a viscous fluid 56.The viscous fluid may be gel, oil, a jelly or the like. Similarly, theindividual receiver unit 32a is ultrasonically coupled to the containerrim 16 by the same viscous fluid 56. In this manner with the ultrasoniccoupling of the transmitter and receiver to the container rim, a directtransmission of the ultrasonic waves are assured. Hence the system ofFIG. 3 avoids the need to immerse the container rim and transmitters andreceivers in water, such as exemplified in FIG. 2.

FIG. 4 shows another embodiment for ultrasonically coupling theindividual transmitter 30a and individual receiver 32a to the containerrim 16. Suitable elastomeric cups 58 are provided on the ends of thetransmitter and receiver to ultrasonically couple the transmitter andreceiver to the container rims 16. The systems of FIGS. 3 and 4therefore provide ways of ultrasonically coupling the transmitters andreceivers to the container rim to determine the integrity of thecontainer seal without having to immerse the container in water or otherultrasonic coupling medium.

FIG. 5 shows a sealed circular rim container 60 which can be tested witha transmitter and receiver array 62 and 64. In this manner, the rim istested at the locations of the transmitters and corresponding receiversto determine the presence of any flaws in the bond of the lid 66 and thecontainer 68. The array of transmitters and receivers 62 and 64 arepositioned about the container rim 70 to detect flaws in the vicinitiesof each of the detectors.

An alternative set up for detecting flaws in the rim 70 of the container60 is to position the rim between a single transmitter 72 and receiver74 of the ultrasonic testing system as shown in FIG. 6. The transmitterand receiver are ultrasonically coupled to the rim, for example, by thetechniques of FIGS. 3 or 4. The container 60 is then rotated in thedirection of arrow 76 in either a continuous or stepwise manner to allowfor transmission of ultrasonic waves to the container rim which are thensubsequently analyzed in accordance with the procedure to be laterdescribed.

It is appreciated that a variety of other transmitter and receiverarrays may be used to provide, for example, better coverage, improvedsensitivity, cost economies and the like. Such conditions may bedependent upon the characteristics of the seal to be detected. Variousconsiderations include, for example, as an alternative to FIG. 6, thecontainer may remain stationary and the transmitter receiver pair movedin a manner to trace the circumference of the container rim and therebysense defects in the seal of the container rim. The transmitter andreceiver arrays, such as shown in FIG. 5, can either be arranged toprovide for discontinuous coverage with the spaced-apart positioning ofthe transmitters and receivers, or a continuous coverage where thetransmitter receiver arrays are positioned very close to one another,normally proximate to each other to provide for complete coverage of theseal area. For some container configurations, a continuous or evendiscontinuous transmitter receiver array may be too costly. It iscontemplated, in accordance with this invention, that half of thecontainer rim is covered by the array of transmitters and receivers.Either the sensor system or the container is then rotated 180° tocomplete scanning of the other half of the container rim.

It is also appreciated that, with multiple receivers and transmitterssuch as the arrangement of FIG. 5, it is not necessary that the receiverbe directly aligned with the transmitter. It is possible to offset thereceivers relative to the transmitter to enhance the coverage of thecontainer rim seal. As shown in FIG. 5A, the staggered arrangement forthe transmitters 62 relative to the receivers 64 is such that eachreceiver is positioned between the transmitter 62 in terms of theirgeneral direction of transmission. Alternatively as shown in FIG. 5B,two receivers for every transmitter may be provided. Transmitter 62 isthen located above two receivers 64 where the receivers are close toeach other and generally aligned with the transmitter. Such arrangementprovides for improved sensitivity in detecting flaws in the containerseal. This arrangement also indicates another advantage of the inventionin that the container rim does not have to be centered exactly betweenthe transmitter and the receiver. Considerable leeway is permittedparticularly with the immersion applications where a gap of up to 5 mmcan exist. On the other hand, with prior art systems such as the echotechnique, a precise location of the bond surface is always requiredrelative to the transducer.

As shown in FIG. 5C, the transmitter may be either a single element or adual element transducer. Such dual element transducer 63 transmits theultrasonic waves through the container rim 70. Instead of locatingreceivers on the other side of the container rim, a reflective surface71 is provided to reflect the ultrasonic waves back through thecontainer rim to be received by the receiving portion of the dualelement transducer 63. This is in keeping with the invention where theultrasonic waves are transmitted through the rim and then reflected backthrough the rim by a suitable reflective surface 71.

As noted, the variations on the types of transmitters and receivers usedin accordance with this invention may to some extent be based on thetype of containers. It is appreciated that the lid may be foil, wherethe base is laminated or non-laminated. As an alternative, the lid maybe laminated or non-laminated multilayer plastic and the base may befoil. Alternatively both the lid and the container may be multilayerplastic of either laminated or non-laminated construction.

As shown in FIG. 5D, the continuous transducer array provides for aplurality of adjacent transmitters 62 with corresponding opposingreceivers 64. The transmitters and receivers are positioned directlybeside each other where their array is such to conform, in thisembodiment, to the rectangular shape of the container rim 70. Althoughthis array is cost intensive, it does provide for the best coverage indetecting the flaws in the container rim seal. Such detection may bewarranted in situations where the contents are of significant value,such that the shelf life is an important consideration. It isappreciated that the reflective system functions in the same manner asthe other transmitter and receiver systems. The transducer system isadapted to receive only wave energy reflected by the reflective surface71. This system therefore requires the transmission of the wave energythrough the rim to accomplish detection of minute particles in the sealwhich can cause flaws.

An example of an apparatus for positioning the transmitter 72 and thereceiver 74 on the rim 16 of the container 18 is shown in FIG. 7. A base78 supports a standard 80. A spring-loaded clip mechanism is provided asmounted on the standard 80. A clip mechanism 82 comprises a firstsupport arm 84 to which the transmitter 72 is secured. A second supportarm 86 is provided to which the receiver 74 is connected. A second bar88 is provided having springs 90 and 92 at each end thereof and whichextend through the arms 84 and 86. The springs 90 and 92 providesufficient pressure on the arms 84 and 86 relative to their mounting onthe standard 80 to locate the transmitter 72 and receiver 74 on opposingsides of the container rim. The transmitter and receiver areultrasonically coupled to the container rim in accordance with theprocedures of either FIGS. 3 or 4.

The container 18, as mounted on table 94, is rotated to pass therectangular-shaped rim 16 between the transmitter and the receiver 72,74. The table 94 is provided with a suitable cam mechanism to rotate thecontainer through a prescribed pattern so that the entire circumferenceof the rim 16 is scanned. As with the scanning procedure of FIG. 6, thecontainer is either continuously moved or sequentially moved to providetransmission of ultrasonic waves through the container rim and hencedetect any flaws therein.

A block diagram of the electronic components of the seal inspectionapparatus is shown in FIG. 8. Inspection of the seal area of a flexiblepackage is carried out by transmitting ultrasonic waves through thecontainer rim. These waves are generated and detected by two arrays ofultrasonic transducers 30 and 32; i.e., transmitters and receivers,placed on the opposite sides of the container seal region 16. In orderto improve the transfer of acoustic energy from the transducers, a thinlayer of water 50, such as in FIG. 2, is maintained between thetransducer surface and the seal surfaces. The generation and detectionof the ultrasonic energy is achieved by a pulser/receiver 98 via anamplifier 96, such as is conventional with ultrasonic inspectiondevices. The pulser/receiver may produce 100/200 volts D.C. pulses at apulse repetition frequency in the range of 1-10 kilohertz with a bandwidth from 100 KHZ to 50 MHZ in a typical arrangement. The ultrasonictransducer array is connected to the signal generation and detectionequipment via a multiplexer 102 which activates each transducer unit inthe array sequentially as shown by multiple leads 103a, b, c, . . . n.

The signals detected by the transducers are rectified to produce a videosignal. These signals are then passed through a series of gates 100,such that the signals which contain information about the seal regionare windowed. The peak and the width of the windowed signal may then beevaluated at 104 and subsequently be subtracted from a reference signaltaken from a look-up table 106. The look-up table is compiled fromaveraged signals from a container with known seal integrity. Thedifference of the signals may be indicated on a display monitor by colorcoded lights 102. The magnitude of such difference indicates the qualityof the seal integrity. The difference, once exceeding a predeterminedmagnitude, indicates a flaw in the seal. This information may also bedigitized by an "analog to digital" convertor for electronic storage andfurther analysis in unit 110.

The voltage signals generated by the gates 100 of the electronic systemof FIG. 8 are shown in FIGS. 9(A,B), 9(C,D) and 9 (E,F). For eachsignal, the information which is considered relevant to determiningdefects is located in the center part of each graph. The right-hand sideof the graph shows secondary effects, that is, stray echoes and are notconsidered relevant to the determination of a defect. When the containerrim is free of defects, the first peak in the central portion of thegraph is of considerable height. In each graph, a horizontal upper linedefines signal magnitude which corresponds to a defect-free seal. Hence,when the height of the first peak is close to this upper line, thenthere is no defect. However, when the first peak appears considerablybelow the upper horizontal line, a defect is present.

With reference to FIG. 9A, the signal generated by a defect-free rimdemonstrates that the first significant peak is slightly above the upperhorizontal line. However in FIG. 9B, the first significant peak issubstantially below the upper horizontal line to indicate the presenceof silicon grease in the seal area which has resulted in a defectiveseal. Similarly, in FIGS. 9C and 9D, the comparison of the defect andhence significantly lower first peak in FIG. 9D, graphicallydemonstrates the ability to detect Teflon in the seal. As shown in FIG.9C with the defect-free rim, the first peak is well above that of thedefective seal and as noted, is slightly above the upper horizontalline.

FIGS. 9E and 9F demonstrate the detection of meat fibers in the seal.Normally, this is very difficult to detect; however, with the systemaccording to this invention, the presence of a meat fibre in the sealstands out significantly. In FIG. 9E, the defect-free rim has the firstsignificant peak very close to the upper horizontal line. However inFIG. 9F, the first significant peak is roughly one-half the height ofthat in the defect-free rim to indicate the presence of meat fibredefects. Hence this invention is capable of detecting not only the verydifficult to determine silicon and Teflon types of defects, but also thepresence of very fine meat fibers in the seal.

It is understood, of course, that this invention is particularly suitedto the measurement for meat fibres. This is the most common form of foodwhich develops flaws in the seal. The above examples, however, alsodemonstrate the effectiveness of this invention in detecting silicongrease and Teflon. To demonstrate the sensitivity of the method withthis type of sensitivity, it is appreciated that many other types offood contaminants which affect the quality of the seal can be measuredwith this invention. With the examples of FIGS. 9E and 9F, the testswere run with approximately one square mm of meat fibre mix positionedon the bond line and the bond line was then sealed using a transparentplastic lid material. This resulting defect in the seal is of such aminuscule nature to be barely visible to the naked eye. However, asdemonstrated with respect to FIG. 9F, the flaw was easily detected bythe process and apparatus of this invention.

As noted, the upper horizontal line in each of FIGS. 9A through 9F isused as a reference line to judge the height of the transmitted soundpulses. It is understood that, under actual production conditions,various techniques may be employed to determine the height of thehorizontal line. For example, statistical process control may beemployed using a representative sampling of the containers passedthrough the device. The desired confidence level can be calculated toposition electronically the horizontal line. The distance between thetwo vertical lines of the peak would be set before hand on theinstrument to define the time interval of interest. This distance wouldconstitute a "gate" where the instrument used would be a normal form ofa gated peak detector. Hence the position of the peak within the gate isirrelevant. A reject signal would be transmitted if any peak does notreach or go beyond the upper horizontal line.

Although preferred embodiments of the invention have been describedherein in detail, it will be understood by those skilled in the art thatvariations may be made thereto without departing from the spirit of theinvention or the scope of the appended claims.

We claim:
 1. A method for determining bond integrity of a sealed packagehaving a lid bonded to a container rim by detecting flaws in the bondbetween the lid and the container, said method comprising:i) positioningsaid container rim between an ultrasonic transmitter system and anultrasonic receiver system; said transmitter system and said receiversystem comprising an array of a plurality of transmitters and acorresponding plurality of receivers, said array having a spatialarrangement to correspond to a circumferential shape of said containerrim and thereby locate said transmitters and receivers at locationsabout said container rim; each of said transmitters being offsetlaterally from a corresponding receiver; ii) ultrasonically couplingsaid transmitter system and said receiver system to said container; iii)transmitting ultrasound waves from said transmitter system through saidcontainer rim to said receiver system while said container rim remainsstationary relative said transmitter system and said receiver system;iv) generating a voltage signal representative of said ultrasound wavesreceived by said receiver system; and v) analyzing said voltage signalfor predetermined signal characteristics representative of a flaw insaid bond to identify a flawed package seal.
 2. An apparatus for use indetermining bond integrity of a sealed package having a lid bonded to acontainer rim, said apparatus comprising:i) spaced-apart opposingultrasonic transmitter system and an ultrasonic receiver system, saidtransmitter system comprising an array of a plurality of transmittersand said receiver system comprising an array of a plurality ofreceivers, said array having a spatial arrangement to correspond to acircumferential shape of said container rim and thereby locate saidtransmitters and said receivers at locations about a container rim, eachof said transmitters is offset laterally from a corresponding receiver;ii) means for positioning a container rim stationary between saidultrasonic transmitter system and said ultrasonic receiver system; andiii) means for ultrasonically coupling said transmitter system and saidreceiver system to a container rim.
 3. A method for determining bondintegrity of a sealed package having a lid bonded to a container rim bydetecting flaws in the bond between the lid and the container, saidmethod comprising:i) positioning said container rim between anultrasonic transmitter system and an ultrasonic receiver system; ii)ultrasonically coupling said transmitter system and said receiver systemto said container rim; iii) transmitting ultrasound waves from saidtransmitter system through said container rim to said receiver system;iv) generating a voltage signal representative of said ultrasound wavesreceived by said receiver system; v) analyzing said voltage signal forpredetermined signal characteristics representative of a flaw in saidbond to identify a flawed package seal; vi) said transmitter system andsaid receiver system having an array of a plurality of transmitters andan array of a plurality of receivers, said array having a spatialarrangement to correspond to a circumferential shape of said containerrim and thereby locate said transmitters and receivers at locationsabout said container rim, said array comprising two receivers for eachtransmitter, the two receivers being offset laterally relative to saidtransmitter.
 4. An apparatus for use in determining bond integrity of asealed package having a lid bonded to a container rim, said apparatuscomprising:i) spaced-apart opposing ultrasonic transmitter system and anultrasonic receiver system; ii) means for positioning a container rimbetween said ultrasonic transmitter system and said ultrasonic receiversystem; and iii) means for ultrasonically coupling said transmittersystem and said receiver system to a container rim; said transmittersystem including an array of a plurality of transmitters and saidreceiver system comprising an array of a plurality of receivers, saidarray having a spatial arrangement to correspond to a circumferentialshape of said container rim and thereby locate said transmitters andsaid receivers at locations about a container rim; wherein said arraycomprises two receivers for each transmitter, the two receivers beingoffset laterally relative to said transmitter.